MILLIONS of motorists’ vehicles may be at risk of corrosion because of the method that Surrey County Council uses to de-ice roads, research by a car manufacturer has suggested.

A study by Volkswagen found that the process of spreading a mixture of brine and salt on icy roads could be damaging to vehicles.

The method, which is known as pre-wet, is already used by the county council and will be rolled out on all major roads across the UK this winter following its adoption by the Highways Agency.

The Volkswagen research over the past three years has identified possible links between the pre-wet method and car corrosion.

The study looked at the number of warranty claims made by Volkswagen customers in areas of Austria between 2003 and 2006, and it found that they went up significantly in places where the pre-wet salt was used.

It is therefore believed that this method of de-icing roads, which involves more water, could cause rusting to the underside of cars, blemish paintwork and damage alloy wheels.

Engineering publication Surveyor believes that the Volkswagen study provides enough evidence to prove that pre-wet is damaging to cars, which in turn is lowering their value.

Editor Adrian Tatum said: “It is vital we make UK roads safer during tough conditions, but if this particular technique used to grit the roads is potentially leading to corrosion of vehicles and street furniture, then something is quite clearly wrong and this issue has to be addressed.

“The pre-wet is put on in the mornings or evenings when it’s moist anyway, and because there’s more moisture it means there’s more splashing. When cars are driving through brine and salt, it attaches itself more easily to the car.

“I wouldn’t necessarily say the council should change the method, but we’d like to see them review the situation they’ve got at the moment.”

Every year Surrey County Council spends £2m de-icing roads during the winter. At the beginning of the season the authority stockpiles about 13,500 tonnes of salt. Surrey was one of the first highways authorities in the country to adopt the pre-wet salt method in 2000, following a study of salting operations in Sweden.

A spokesman said the wetted salt was more effective in preventing ice forming than traditional dry salt., meaning safer roads.

And according to the council, because wetted salt remains in place it means that the number of salting trips made each winter is fewer, which saves money.

The spokesman said: “Unlike the traditional dry salt granules, there is little, if any, risk that wetted salt will damage windscreens or vehicle bodywork when gritters are spreading the salt.

"As a result, claims are substantially reduced, or eliminated altogether, and drivers do not suffer this form of damage to their vehicles.

"As a rule the Highways Agency has been fairly conservative in their approach to adopting new methods and materials. The fact that they have now moved to wetted salt provides a strong stamp of approval for this method.”